Glossary of Network Terms

Click on a letter to navigate to that section of the glossary.

10Base2 - Shared Ethernet distributed in a "daisy-chain" fashion from one workstation to the next using BNC tee-connectors and coaxial cable. Also known as "thinnet". The second-oldest form of commercial Ethernet.

10Base5 - Shared Ethernet distributed over a special coax then tapped via transceivers which attach to the cable. The oldest form of commercial Ethernet.

10BaseT - A variant of Ethernet connecting stations via unshielded twisted pair cable using RJ-45 connectors, running at 10 Mbps. Deployed in a "star" topology, so-called because connections originate from a common point, the networking device, which may either be a hub or repeater (shared Ethernet) or a switch (switched Ethernet).

100BaseT (100BaseTX) - A variant of Ethernet connecting stations via Category 5 unshielded twisted pair cable, also with RJ-45 connectors, but running at 100 Mbps. 10 Mbps. Deployed in a "star" topology, so-called because connections originate from a common point, the networking device, which may either be a hub or repeater (shared Ethernet) or a switch (switched Ethernet).

ASCII - Acronym for American Standard Code for Information Interchange. ASCII is an ANSI character set. The standard ASCII character set consists of 128 decimal numbers (0-127) for letters of the alphabet, numerals, punctuation marks, and common special characters. The extended ASCII character set extends to 255 characters and contains special mathematical, graphics, and foreign characters.

Asynchronous Communications - A method of transmission in which one character is sent one bit at a time; also referred to as serial transmission.

Asynchronous Transfer Mode (ATM) - A high speed, connection-oriented switching and multiplexing technology for transmitting information across a wide area or local area network in units called cells. ATM divides information up into fixed-length cells capable of transmitting several different types of traffic simultaneously. It is asynchronous in that information streams can be sent independently, without a common clock. ATM can be described in three planes: The user plane coordinates the interface between protocols and ATM; The management place coordinates the layers of the ATM stack; and the control plan coordinates signaling, setting up and tearing down virtual circuits.

AUI connector - A networking connector that can be used with a transceiver to connect various kinds of cables such as fiber optic (10BaseF), thick coaxial (10Base5), thin coaxial (10Base2) and UTP (10BaseT).

bps - Bits per second. To convert to bytes per second, divide by 8.

Bytes per second - Bytes per second. To convert to bits per second, multiply by eight.

Backbone - The generic term for LAN or WAN connectivity between subnetworks across the enterprise. Generally a conduit for traffic between multiple networks which must operate at an order of magnitude greater speed and capacity than the networks it connects. Backbones are generally bordered by either switches which consult routers or by routers.

Bandwidth - This is the range of signal frequencies that can be carried on a communications channel. While this indicates the channels information carrying capacity, it is more commonly expressed in bits per second (bps), or mega (million) bits per second (Mbps). When one says bandwidth increases, one means that network capacity and perhaps speed has gone up.

Bus topology - A network topology in which nodes are connected to a single cable with terminators at each end.

Cable Plant - The physical infrastructure (wire, connectors, cables, etc) used to carry data communications signals between data communications equipment.

Category 5 - A standards-based cable consisting of twisted-pair wire, with a specific number of twists per foot to reduce electrical crosstalk and provide a specific characteristic impedance (capacitive and inductive reactance) per each foot of cable. Used as an industry standard for modern cable plant, and required for Fast Ethernet. Desirable for 10BaseT as well.

CCITT - Consultative Committee for International Telephone and Telegraph. This advisory organization is part of the ITU (International Telecommunication Union) which is an agency of the United Nations. Organization recently renamed International Telecommunications Union-Telecommunications Standard Sector (ITU-T)

CSMA/CD - Carrier Sense Multiple Access with Collision Detection. CSMA/CD is the access method used in Ethernet where nodes contend for the right to send data.

Desktop - Generally considered to mean the confluence of a work location, a desk area and a computing device, distinct from a lab, which may have many computing devices. Intended to refer to one computing device, PC or workstation, which uses one network connection.

Ethernet - Also known as CSMA/CD, it is a networking technology which relies upon collision detection to back off from simultaneous transmission. Operating at 10 Mbps, 100 Mbps (Fast Ethernet) and 1000 Mbps (Gigabit Ethernet), it is the single most commonly deployed networking technology in the LAN, and the primary one used in UCInet LANs. Ethernet is a layer-2 technology.

Ethernet Switch - A networking device which provides switched Ethernet. (see Switched Ethernet).

FDDI - A network based on a backbone of dual counter-rotating 100 Mbps fiber optic rings. One of the rings is normally designated as the primary, the other as the secondary. This even holds true if one of the point-to-point fiber optic segments becomes disabled. The counter-rotating rings are connected to single-fiber slave rings through concentrators. Bypassing inactive stations is accomplished with fiber optic switches. FDDI allows higher utilization than Ethernet. One of several technologies used in the UCInet backbone.

File Server - A device on a LAN that provides mass storage of files. A file server can be dedicated (only performs network management functions) or non-dedicated (where user applications can co-exist while the network is available.

File Transfer Protocol - The Internet (TCP/IP) protocol and program are used to transfer files between hosts.

Gbps (Giga bps) - A billion bits per second.

Hub - The center of a star topology network or cabling system containing workstations, servers or peripherals. The term Ethernet hub typically refers to a shared-media hub. Sometimes referred to as a repeater. Supports shared Ethernet in a "star" topology over Category 5 twisted-pair wire terminated by RJ-45 data jacks.

IEEE 802.3 compliant - Complying to the standards for 10 Mbps networks established by the Institute of Electrical and Electronic Engineers (IEEE)

Internet - The Internet; successor to DARPA-NET. Worldwide internetwork based on the TCP/IP protocol.

Internet Protocol (IP) - Part of the TCP/IP protocol suite. The layer three protocol used in a set of protocols which support the Internet and many private networks. IP provides a connectionless datagram delivery service for transport-layer protocols such as TCP and UDP. Part of the TCP/IP protocol suite. This is the supported protocol on UCInet.

Jabber - This occurs when there are excessively long data packets being transmitted from the node (i.e., workstation, server). At that point, the hub, or concentrator, partitions (isolates) the node from the network until the condition is corrected.

Jabber protection - A feature of some networking hubs that ensures your network won't go down due to excessively long data packets.

Kbps - (Kilo bps) - A thousand bits per second or kilobits per second. A measurement of the transmission speed of data measured in 1,024 bits per second.

LAN - See Local Area Network.

Leased Line - Also referred to as a private line. A leased line is obtained from a communications company (carrier) to provide a transmission medium between two points. The line consists of a permanent dedicated circuit between two points, or to set of previously arranged points. The cost of the line is usually based on the distance between locations. This is in contrast to switched or dial-up lines, which can be connected to any point on the network.

Local Area Network - (LAN) - A network, typically Token Ring or ATM, typically confined to a limited geographic area, with moderate to high data rates (100kbps to 100Mbps) which connects together multiple computers, printers and other network devices in a departmental or workgroup setting. It may be connected to other LANs via a backbone, typically through a router or routing device, or connected to a through a router to a WAN connection to other networks, such as the Internet.

Loopback Tests - There are four types of loopback tests which are as follows: (1) the local digital loopback tests the operation of the DTE, including whether or not data is leaving the terminal or computer port; (2) the local analog loopback tests the digital and analog circuits of the modem; (3) the remote digital loopback checks the operating condition of the line and remote modem; (4) the remote analog loopback tests the line to the remote modem.

Mbps - (Mega bps) - A million bits per second. A measurement of the transmission speed of data measured in 1,048,576 bits per second.

MAC Address - The hardware address of a device connected to a network. In Ethernet, the Ethernet address.

Micro segmentation - The technique of splitting up shared network segments by deploying switching to reduce the size of the collision domain, reduce congestion and improve throughput.

MTA - Mail Transport Agent. Unlike an MTC, the MTA actually handles sending and receiving the email to and from the system it is based upon. Most MTAs support aliasing and forwarding, as well as either the POP or IMAP protocols for clients which do not have standard MTA support upon their computer. MTAs which support POP and/or IMAP are referred to as mailhosts, and often support other functions. At UCI, MTAs are used to accept mail from the network and the outside world, then forward the mail to specific places. Mail address to user-id@uci.edu goes through campus MTAs for translation to delivery points, and actual delivery.

MTC - Mail Transport Client. Provides a user-interface for the management of email received, or the creation of it.

Multicast - A form of broadcast where copies of a packet are delivered only to a subset of all possible destinations.

Multicasting - Directing a message or a packet to some subset of all stations on a network by the use of a special destination address.

Network Segment - A portion of a network set apart from other network sections by a bridge, router or switch. Each network segment supports a single medium access protocol and a pre-determined bandwidth. The more stations are on a network segment the more divided this bandwidth is. Crowded network segments lead to a condition known as congestion, where performance declines. An electrically continuous piece of a bus based

LAN. Segments can be joined together using repeaters, bridges or routers. Segments may also be split apart using the same devices. The use of switches to break up segments is known as micro segmentation. See also shared and switched Ethernet.

Network topology - The arrangement of nodes usually forming a star, ring, tree, or bus pattern.

NIC - Network Interface Card. A board in your PC that has one or more ports for connection to a network.

Node - Any device including servers and workstations connected to a network; also the point where devices are connected.

Non-Volatile RAM - Also NVRAM. Random access memory whose data is retained when power is turned off. This is especially useful for modems to store user-defined default configuration settings and frequently used telephone numbers. This information would be loaded into modem RAM at power-up.

On-Line State - Same as data mode. To transmit or receive data, the modem must be in the on-line state. When placing a call, the modem is put on-line with the dial command.

Packet - A collection of bits comprising data and control information formatted for transmission from one node to another.

Packet Sniffer - A machine (usually a laptop with special software) that anylizes all packets that traverse across the wire of the network where connected. Used to diagnose network related problems between all active stations on a network.

Protocol - A standardized set of rules that specify the format, timing, sequencing, and/or error checking for data transmissions.

Pulse Dialing - Also referred to as rotary dialing, i.e., dialing with the older-style rotary dial wheel. The dial modifier ATDP sets the modem to pulse dialing, which is the default method as opposed to tone dialing (push-button touch-tone) which is enabled with ATDT. All telephone exchanges will accept older-style pulse dialing and most exchanges will accept modern tone-dialing. Tone dialing is faster and more reliable since mechanical relays and their inherent failure mechanisms are avoided.

QoS - See Quality of Service.

Quality of Service - This is a networking term which may be used in one of two ways. In the first way, it represents a quality of networking. In the second, referred to usually as "QoS", it represents a guarantee or commitment to not only a particular quality of network service but also a particular rate or minimum rate of data delivery, as well as maximum times between packets of data. Used where applications are sensitive to delays, such as video conferencing. Initially a feature of ATM, it is now being incorporated into the TCP/IP protocol and will eventually be available as a service on non-ATM networks. A statement that QoS is is provided is distinct from one which says QoS guarantees are provided. UCInet provides a good quality of service, but not QoS guarantees as part of Basic Network Services.

Repeater - Used to extend the topology, allowing two or more cable segments to be joined. In a 10Base-T network, the repeater provides the central connection point where the gathering of statistics and network management functions take place.

Result Code - A response sent by the modem after executing a command. The response reports the modem's status or the progress of a call and can take the form of either digits (numeric) or words (verbose). Issuing a V1 command enables word responses. A V0 (V-zero) command enables numeric responses. The Q1 command disables their use entirely. Example: "OK" (word), or 0 (numeric) indicates that the modem successfully executed a command.

Ring Topology - A network topology in which nodes are connected in a closed loop; no terminators are required because there are no unconnected ends.

RJ-45 connector - A connector utilized in 10BaseT and 100BaseTX networks with UTP cabling.

ROUTING - The function of determining the route a packet should take from a subnet to get to another subnet. A component function of all internetworks, or internets. The process of delivering a message across a network or networks by the most appropriate path.

Route - The patch that network traffic takes from its source to its destination.

Router - A system responsible for making decisions about which of several paths network traffic will take, and for keeping track of routing information which is being passed along a network be one of several different possible protocols. To do this a router uses a routing protocol to gain information about the network and uses algorithms to choose the best router based on several criteria known as route metrics. In OSI terminology, a router is a Network Layer intermediate system. See also IP router.

Shared Ethernet - A network segment which has multiple nodes connected, and where available bandwidth is divided among users in a dividing effect. May be deployed using 10Base5, 10Base2 or 10BaseT (the latter being a hub). The most widely deployed technology in UCInet.

Simple Network Management Protocol (SNMP) - Both a way of obtaining and storing information about network devices. A protocol designed to manage networking devices. SNMP capable devices keep statistics on their operation, if instructed to do so, which may be remotely fetched and analyzed by central management stations.

RTS/CTS - Request to Send/Clear to Send. RTS and CTS are two control signal lines between the modem (DCE) and terminal (DTE) which allow the terminal to control the flow of information. See also flow control.

Standard AT-Command - The basic AT command set, originated by Hayes Microcomputer Products, Inc.

Subnet - A portion of a network, which may be physically independent, that shares a network address with other portions of the network and is distinguished by a subnet number. Subnets are created and supported by the use of routing.

Switch - A device which logically connects to network stations through a network fabric. See also Switched Ethernet.

Switched Ethernet - An Ethernet technology deployed from a central box over Category 5 twisted-pair wire or fiber optic, and which allows the full utilization of bandwidth for each network conversation by switching connections point-to-point between stations talking to each other, providing in effect a dedicated connection. Considered to be an order of magnitude faster than its shared counterpart.

Synchronous Communications - A method of transmission in which data bits are sent continuously at the same rate under the control of a fixed frequency clock signal.

T-Connector - A T-shaped device with two female and one male BNC connectors used with coaxial such as 10BASE2..

Terminator - 50-ohm coaxial plug used to attach to one end of a BNC T-connector when the associated station is first or last in the group.

thin coaxial cable - A networking cable with BNC terminators used on 10Base2 networks.

TCP/IP - Transport Control Protocol / Internet Protocol. The protocol of the Internet and most internets and many intranets.

Topology - The physical layout of a network. The principal LAN topologies are bus, ring, and star.

Transceiver - An AUI (Attachment Unit Interface) device for receiving and transmitting data that often provides collision detection as well.

Transmission Control Protocol - A layer-four protocol in the set of protocols which support the Internet and many private networks. TCP is the TCP portion of TCP/IP, and provides a guaranteed transport service.

Twisted-Pair cable - A wiring scheme with one or more pairs of 18 to 24- gauge copper strands as used in 10BASET and others.

UTP cable - An abbreviation for unshielded twisted-pair cable. A networking cable with RJ-45 connectors used on 10BaseT and 100BaseTX networks.

VLAN - See Virtual Local Area Network.

Virtual Local Area Network - Individual workstations, rather than being directly connected to a shared media, are instead connected to an intelligent device such as a switch which has the capability through software to define LAN membership. This permits a systems administrator to resegment the LAN without changing the physical arrangement. It also allows, with some switching technologies, the ability to support multiple subnets on a single switch where a series of router interfaces were previously required.

WAN - See Wide Area Network.

Wide Area Network - A network which covers a larger geographical area than a LAN or a MAN and where telecommunications links are implemented, normally leased from the appropriate Private Telephone Operator(s). Examples of WANs include packet switched networks, public data networks and Value Added Networks (VANs).

WAN Connection - A network connection, usually through a router or an ATM switch, which connects two geographically distanced networks together.

XON/XOFF - XON and XOFF are the names of two different flow control characters. See also flow control.